There are different types of known dynamometers, dynamographs, ergographs, some of which are mechanical and others of which are mechanical-electrical or mechanical-electronic devices. As a rule, all of these devices operate based on the correlation between the fatigue stage of the organism and its resistance to effort. By initial measurement by a suitable method of the resistance to effort, for instance that of the hand-flexor muscles, before performance of physical or intellectual work, and by a subsequent measurement after completion of the work, one finds that the resistance effort of the muscles diminishes. The diminution of the resistance effort of the respective muscles is especially marked as the overall tiredness, because of the work, of the human organism is greater.
The various dynamometers or dynamographs have various shortcomings that limit their performance and utility.
For example, they cannot establish the effort which serves to provide the measurements with a given rhythm. Since they are incapable of imposing a certain rhythm on the activity of the test subject, the tests are nonreproducible under given conditions, causing arbitrary results upon repetition of the tests with the same subjects and leaving possibly erroneous conclusions. Since it is not possible to impose upon the subject a movement-execution rhythm, the rhythm cannot be varied in spite of the fact that adjustment of the rhythm of the effort makes it possible to choose a rhythm that is the best for each individual subject.
Conventional devices also do not have the capacity to indicate the length of the experimental efforts, although the time factor is extremely important with respect to measurement of the resistance to effort.
Another drawback of known dynamographs is that it is impossible to rigorously check the movements executed by the subject, especially to the extent that it is possible to establish that the tests are reproducible and that a full effort has been exerted at each cycle by the subject.